In a photodetection element such as an avalanche photodiode or a silicon photomultiplier (hereinafter also referred to as SiPM), photon detection efficiency (also called PDE) has a high temperature dependence. Therefore, in a case where a photodetection element is used outdoors like an on-vehicle photodetection element, the chip needs to be maintained at a constant temperature with the use of a chip temperature monitor such as a thermistor, and a Peltier element or a heater or the like. As a result, the device becomes larger in size, and power consumption also becomes larger. Furthermore, a temperature monitor formed with a different chip from the main body of the photodetection element has a poor accuracy in reproduction of an actual device temperature, and causes a decrease in temperature correction accuracy.
The photon detection efficiency of a SiPM is expressed by a product of the aperture ratio S of the device, the photoelectric conversion efficiency q, and the avalanche probability Pav. The avalanche probability Pav that has large influence as temperature characteristics can be expressed experientially asPav=P0×(1−exp(−a×Vov)).Here, “P0” is a constant that does not depend on temperature, and “a” is a constant attributed to the device structure. Meanwhile, the voltage Vov is expressed asVov=Vop−Vbd,where Vbd represents the breakdown voltage Vbd of the device, and Vop represents the drive voltage Vop of the device.
Therefore, in a case where the drive voltage Vop is constant, the breakdown voltage Vbd changes. As a result, the voltage Vov changes, the avalanche probability Pay changes, and the temperature dependence of photon detection efficiency appears. In view of this, to reduce the temperature dependence of photon detection efficiency, the temperature dependence of the breakdown voltage Vbd needs to be corrected.
The breakdown voltage Vbd of a photodetection element (photodetection device) normally exhibits substantially linear variation with device temperature. As is apparent from this, temperature correction can be performed. However, the influence of variation of the breakdown voltage Vbd between devices cannot be ignored, either. Therefore, in a case where a large number of pixels are employed as in a SiPM, it is also necessary to correct variation of the breakdown voltage Vbd of each pixel.